1. Field of the Invention
The invention generally relates to a heat-dissipating system and a control method thereof, and more particularly, to a heat-dissipating system and a control method thereof able to decrease fan noise and advance heat-dissipating effect.
2. Description of Related Art
During running an electronic apparatus, its internal electronic components, such as the computer's central processing processor (CPU) or the light source in a projector, generate heat. To avoid heat accumulation that causes an excessive temperature inside the electronic apparatus and results in electronic apparatus crash or damaging the electronic components, a heat-dissipating system is required to dissipate heat.
In general, the heat-dissipating system uses at least one fan to create air circulation so as to achieve heat-dissipating effect through the air circulation. However, when the fan is running, in addition to causing air circulation, the fan also generates noise. Therefore, when using the fan for cooling, in addition to considering the cooling effect, the noise generated by the fan is also considered to avoid excessive noise causing the user's discomfort.
When the heat-dissipating system uses more than one fan, the fans are used in parallel way to increase the air-flow. In consideration of cost, these fans are driven by a fan driver, and the fan driver normally controls all the rotation speeds of the fans by taking the rotation-speed of one of these fans as a reference value. However, if the structure of each fan is the same, each fan is operated with an actual operation error, that under the controls of the same control signal, the rotation speed of each fan can not be all the same. Therefore, under the situation where the fan driver uses the rotation-speed of one of the fans as the reference value to control all the rotation speeds of the fans, the fan driver can not accurately control all the rotation speeds of the fans to fall in an allowable speed range. As a result, the integral heat-dissipating capacity of the fans may be too low or the entire noise is too high.
For example, U.S. Pat. No. 7,714,524 discloses a system and a method for controlling multiple D.C. fans, which includes a plurality of motors, a plurality of driving circuits and a processor, in which these motors are used to rotate the corresponding fans, each driving circuit provides a current to the motor to control the rotation-speed of the corresponding fan according to a pulse modulation signal generated by the processor. The processor herein adjusts the rotation-speeds of the motors based on the rotation-speeds detected by speedometers respectively corresponding to each motor.
U.S. Patent Application No. 20090304199 discloses a system of multiple fan acoustic interaction control. The system includes two fans disposed in parallel, a controller and a power supply. The controller monitors the rotation-speeds of the fans through speedometers and adjusts the rotation-speeds of the above-mentioned two fans so as to eliminate the interactive interfered noise generated by the two fans according to the difference between the rotation-speeds of the two fans, in which the controller can adjust the rotation-speeds as per the priorities of the above-mentioned two fans.